High frequency network



May 21, 1935. I B. D. H. TELLEGEN 2,002,193

HIGH FREQUENCY NETWORK Filed Oct. 28, 1951 2 sheets sheet 1 Iv ll INVENTOR BERNARDUS D.H.TELLEGEN ATTORNEY y 1 B. D H. TELLEGEN 2,002,193

' HIGH FREQUENCY NETWORK Filed 001.. 28, 1931 2 Sheets-Sheet 2 INVENT R 553$? D.H.TELLE,GEN v I BY ATTORNEY Patented May 21, 1935 Bermn'dus Dominicus Hubertus Tellegen, Eindhoven, Netherlands,

assignor to Radio Corporation of America, a corporation of Dela- AppIication 'October 28,

1931,} Serial N... 571,510

In theNetherlands April 25, 1931 M v I 7 3 laims. Ifhe "inventionrelates to a tunable oscillatory. system consisting of capacitively coupled circuits, and it has for its object to provide a tunable system in which-the coupling varies with the tuning in a predetermined desired manner. According to the invention, in order to attain thispurpose useis made of a system comprising a combination of a capacitive coupling whose strength increases with the frequency, and a capacitive coupling whose strength decreases with the frequency. Ajudicious choice of the relative strength of the two couplings allows of keeping the coupling substantiallyconstant for the whole region to whichthe system can be tuned. On

" the other hand, the strength of the couplingmay be caused to vary with the tuning in a predetermined manner if 'such variation should be desired f f fThe novel features which I-believe to be characteristic of my invention are setforth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawings in which I have indicated'diagraminatically several circuit arrangementswhereby my'invention may be carried into effect.

The invention will hereinafter be explained more fully with reference to the drawings which represent some explanatory figures and, by way of example, some embodiments of the invention. Figs; 1 and 2 serve to. elucidate the following considerations on capacitive coupling in general, and,

w .Figs. 3 to 9 inclusive represent byway of example, some embodiments of the system accord: ing to the invention.

. In Fig. 1, two oscillatory circuits L1 01 and 2 or,

I are coupled to one another by means of a condenser'Cs. If the capacity C3 is considerably smaller than thatofCi and On, it can be theoretically shown that the couplingfac'tor k may be represented by the expression: Y

7 Q.; v fi/c c, r

This expression is obtained by neglecting in the exact formula C3 relative to C1 and C2. If the two circuits are tuned. to'the same frequency, the expression for k may be written with the aid of the relation between the resonance fre-' 1 quency w andv the electrlcalmagnitudes of the If the tuning is effected with the aid of the variable condensers C1, C2 and if L1 and L2 remain unaltered, the coupling factor consequently depends on the frequency, which means that the coupling factor increases when the frequency increases. v

;-Fig; 2 represents a circuit arrangement with which the coupling factor decreases with the frequency.'- In this arrangement the coupling is brought about by means of a condenser G4. which is assumed to have a large capacity relative to the variable capacities C1 and C2. In this case the coupling factor It has been foundto be equal to:

. n es/m;

i Figs. 1 and-2 consequently represent types of coupling with strongly different frequency dependency. According to the invention, in order to obtain the desired variation of the coupling factorwith the frequency, the two kinds of coupling. arecombined. A judicious choice of the strength of the different couplings allows in this case of obtaining. a constant coupling, or a coupling which varies withthe frequency ina predetermined manner.

A first embodiment of a circuit arrangement with such. combined coupling is represented, by way of example, in Fig.3. By reason of the conditions above assumed with respect to the values of C4 and C3 relative to C1 and C2, the total coupling' factor may be assumed to be the total amount of the two coupling factors in the cases of Figs. land 2. The coupling factor in the system according to Fig. 3 consequently contains two terms of which one increases with the frequency whereas the other decreases with the frequency.

A judicious choice of the values C3 and C4 renders it possible to obtain, for, example, that over the wholeregion of the tuning the coupling factor varies only slightly. A source of signal energy S may be considered coupled to L1, while a utilization circuit U is coupled to coil L2. "Fig. 4 represents a system in which the coupling factor is independent of the frequency. If in this system C5 is considerably smaller than 01 and C2, and if C6 is considerably larger, the following expression for the coupling factor is found:

Ca L .7 Fig. 5 represents a circuit arrangement of exactly the same kind as that 'of Fig. 4, which however, is made symmetrical by adding two condensers C6 and C7 of which the former is large relative to the tuning capacities, whereas the latter is small relative to these capacities. The coupling factor of this system may be represented as dependent of the tuning frequency.

The most general form of the coupling factor which can be obtained in the manner indicated.

with the aid of fixed capacities is:

The coeficients a, b and c occurring in this expression, may have diiferentsigns, and their: values can be controlled by the choice of, the] values of the coupling capacities.

If in Fig. 3 L1 and c1 or L2 and c2 are inter changed", the two couplings counteract eachother, and the expression for the coupling factor may be written as follows: r

'Thecircuit arrangementshown in Fig. 5 also gives'with the interchange of L1 and C1 or L2 and C2 an inversion of the sign of one of the terms of which consists the expression for the coupling factor. It is evident that thus the course of the coupling factor can be varied in various ways.

Fig. 6 represents a'system with three small oapacities C3, C5, C7 and three large capacities C4, C6, C8. This circuit arrangement may be considered to be produced by combining Fig. 5 with Figs. 1 and 2. The expression for the coupling factor'is found in this case: 7

term which is independent of the frequency there occurs a term which decreases with the frequency,

and a term which increases with the frequency. Fig. 7 represents, by way of example, a circuit arrangement in which the condenser C3 has a slight capacity which is smaller than those of the tuning condensers C1 and C2 while C9 is of the same order of magnitude as C1 and C2. With this arrangement one obtains a coupling factor of the type k=aw b in which a and b are positive constants.

In Fig. 8, C4 is considerably larger than Ci and C2, whereas C10 is of the same order of magnitude as C1 and C2. The coupling factor is now of the pe Finally, in Fig. 9 the capacities C9 and C11 are of the same order of magnitude as the tuning capacities whereas C3 is very small. The coupling factor is now of the type It will be understood, that'in each of the above figures the condensers C1 and C2 may be arranged for simultaneously and similarly tuning the oscillatory circuits with which they are associated. They can obviously be employed between tubes in a radio frequency amplifier, or between an antenna and a tube in a receiver. Further, while I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention fications may be made without departing from the scope of my invention as set forth in the appended. claims.

What is-claimed is: 1. A high frequency coupling network, adaptedfor coupling a preceding source of high frequency-signal energy to a following high frequency load circuit, said network comprising a pair of resonant circuits each including a coil and a variable tuning condenser, one of said coils being magneticallycoupled to the source and the other being magnetically coupled to said load circuit, said variable condensers being adapted for simultaneously and similarly tuning said resonant circuits to a desired signalfrequency, and means, providing a purely capacitative coupling between the resonant circuits which is independent of the tuning of the latter, comprising a fixed condenser, considerably larger than said variable condensers, connected in shunt with the coil and variable condenser in one of said resonant circuits, and a fixed condenser, considerably. smaller than said variable condensers, connected between points of the same 'high frequency potential of the variable condenser, of the other resonant circuit, and the said. shunt fixed condenser.

2. A high frequency coupling network, adapted forcoupling apreceding source of high fre- U-quency signal energy to a following high frequency load circuit, said network comprising a pair of resonant circuits each including a coil and a variable tuning condenser, one of said coils being magnetically coupled to the source and the other being magnetically coupled to said load circuit, said variable condensers being adapted for simultaneously and similarly tuning said resonant circuits to a desired signal frequency, and means, providing a purely 'capacitative coupling between the resonant circuits which is independent of the tuning of the latter,'comprisinga fixed condenser, considerably larger than said variable condensers, connectedin shunt with the coil and variable condenser in one of said resonant circuits, and a fixed condenser, considerably smaller than said variable condensers, connected between points of the same high frequency potential of the variable condenser, of the other resonant oircuit,vand the said shunt fixed condenser, a'second fixed condenser, larger than the magnitudes of the saidvariable condensers, in shunt with the coil and variable condenser of said last named resonant circuit, and a fixed condenser, smaller than said variable condensers, connected between points of the same high frequency potential of the variable condenser of said one resonant circuit and the said second shunticondenser.

'3'. A tunable highfrequency transmission network, adapted to couple a source of signalenergy to a loadcircuit, comprising a pair of resonant circuits each including a coil and'a variable tuning condenser in series, said tuning condensers being adapted to tune said network to a common frequency of a desired frequency range, a first large fixed condenser connected in series with one tuning condenser, a second large fixed condenser connected in series with the other tuning condenser and a third large fixed condenser connected on one side to a point common to both coils and on the other side to a point common to said first and second large condensers, a small fixed condenser in series between each coil of one resonant circuit and the tuning condenser of the other resonant circuit, another small fixed condenser connected between points of the same signal potential of both coils, said three large condensers being each larger than said tuning condensers, and each of said small condensers being smaller than said tuning condensers.

BERNARDUS DOMINICUS HUBERTUS TELLEGEN. 

